Mechaduino is a board that sits on a regular stepper motor and turns it into a servo with a closed loop control of 0.1degree.

Leveraging the Trinamic TMC2208 stepper motor driver gives Ethersweep silky smooth and quiet motor control, which could be very important for some applications.

Oriental Motor of Japan is offering stepper motors with battery-free multi-turn absolute position encoding that can ride through power-loss.